With a continuously growing population, it is becoming increasingly difficult to meet the world's energy needs and, simultaneously, to control carbon emissions to kerb greenhouse gas emissions which are considered responsible for global warming phenomena. These concerns have triggered a drive towards a more efficient use of electricity in an attempt to reduce energy consumption.
One such area of concern is lighting applications, either in domestic or commercial settings. There is a clear trend towards the replacement of traditional, relatively energy-inefficient, light bulbs such as incandescent or fluorescent light bulbs with more energy efficient replacements. Indeed, in many jurisdictions the production and retailing of incandescent light bulbs has been outlawed, thus forcing consumers to buy energy-efficient alternatives, e.g. when replacing incandescent light bulbs.
A particularly promising alternative is provided by solid state lighting (SSL) devices, which can produce a unit luminous output at a fraction of the energy cost of incandescent or fluorescent light bulbs. An example of such a SSL element is a light emitting diode (LED).
It is known to provide SSL lighting devices having a similar overall shape to incandescent light bulbs, for example, bulbous solid state lighting devices. These bulbous SSL devices may be used to replace incandescent light bulbs or used in similar applications to incandescent light bulbs. However, whereas incandescent lighting devices tend to produce a homogeneous luminous distribution close to 360° around the lighting device, solid state lighting elements act as point sources, such that additional measures are required to produce an SSL-based lighting device that is able to produce a luminous distribution similar in appearance to that of incandescent lighting device such as an incandescent light bulb. Without such measures, the SSL-based lighting device may produce a spotty and/or more restricted luminous output. Such a different appearance typically is not appreciated by consumers, and preferably should be avoided or at least minimized in order to improve the market penetration of SSL-based lighting devices.
An example of a LED-based lighting device having a design to improve the uniformity of the luminous output of the lighting device is disclosed in WO 2013/017612 A2. The disclosed LED lighting assembly has a printed circuit board carrying an LED chip, a heat sink thermally connected with the printed circuit board, wherein the LED lighting assembly further comprises a light guide body configured as a bulb, the light guide body having an inner surface, an outer surface as a light emergent surface and an end surface as a light input coupling surface of light from the LED chip. The inner surface is structured so as to form a reflecting surface towards the outer surface to make at least part of light from the end surface to be reflected and exit through the outer surface.
However, this design has some notable drawbacks. Firstly, due to the fact that the LEDs are enveloped by the end surface of the light guide body, the minimum thickness of light guide body must exceed the width of the LEDs. Such a relatively thick light guide body may compromise the luminous efficiency of the lighting device. Moreover, thermal management of the LEDs may become an issue if a relatively large number of LEDs has to be provided on the printed circuit board, for instance to produce a retrofit light bulb having a luminous output equivalent to a 75 W or 100 W incandescent light bulb, due to the intimate coupling between the light guide body and the LEDs. Finally, due to the fact that the light guide body terminates on the printed circuit board, this lighting arrangement is incapable of generating a luminous distribution closely resembling that of an incandescent light bulb.
US2012/327656A1 discloses solid state type light fixtures each having an optical integrating volume filled with a solid light transmissive material. Such a structure does not have a wall with function of a light guide.
US2011/175527A1 discloses lighting applications such as fixtures and bulbs with a light transmissive structure forming a volume. A one piece light transmissive solid, a gel or a liquid is filling the volume. Such a structure does not have a wall with function of a light guide.